等比数列$\left\{a_n\right\}$中,已知对任意正整数n,$a_1+a_2+a_3+\cdots +a_n=2^n-1$,则$a_1^2+a_2^2+a_3^2+\cdots +a_n^2$等于（　　）

唐朝政局可用下图表示，下图中“？”处应为（    ）

keep sb./sth. ＋形容词   使某人/某物保持……   如：

We should ____.我们应该保持我们的城市干净。

keep sb doing sth. 使某人一直做某事

Don't ____.别让我等得太久。

关于城市不同等级的说法正确的是（　　）

    Sambodromo Samba Parade tickets for Rio carnival

    Order on this page your Rio Carnival tickets for the Samba Parade in Rio's Sambodromo.

    Benefit from our unique advantages. Read the Sambodromo ticket and order description first.

Covered Grand Tier Boxes—Yellow on the map

    The boxes in Sector 7 have been covered to offer an enjoyable Parade experience even in the rain. These boxes are more comfortable than the other boxes since the 12 seats are cushioned（带坐垫的）and they also have a coffee table.

    Price for per seat is $ 70.

    Luxury Suite Lounge Carioca—Purple on the map

    The goal of Lounge Carioca in Sector 5 is to reach those who look for a new product to attract, conquer and make new business. It has privileged location -the center of the Avenue! In our cabin we will have ample and comfortable space for our guests to watch the parades in a unique structure.

    Price for per seat is $ 90.

    Luxury Suite Lounge Folia -Red on the map

    This leisure area between Open Front Boxes of Sector 6 and 8 is for 1,000 rather-party-minded people and contains a beauty salon, a dance floor with DJs and has some space also to relax and watch the Parade on a giant screen.

    Price for per seat is $ 100.

    Luxury Suites -Blue on the map

    These covered boxes in Sector 9 are the best places. They are at the right height to offer the perfect view of the Parade, being above the front boxes. You can buy individual seats in the desired suite or rent a whole suite for a particular night.

    Price for per seat is $ 120 and $ 260 for a whole suite.